For those who haven't seen or heard about the film, this eccentric mother-daughter combo -- who were cousins of Jacqueline Kennedy -- were lifted to silver-screen posterity while living with their memories and innumerable cats in East Hampton obliviousness in a rundown 28-room mansion. Three decades later, the Beales now serve as the real-life figures for these seasoned stage veterans to attack with relish. Indeed, as the season progresses, there's likely to be no one available to best Ebersole for the Tony Award.

In the first act, which has been wholly invented by the show's creators, she's giddily imperious as Edith, a woman intent on appropriating the engagement party she's throwing for her debutante daughter (played by the polished Erin Davie, one of two new cast members) and fiancé Joseph Kennedy, Jr. (the suave Matt Cavenaugh). Ebersole's uncompromising portrait of misguided sophistication is that much more effective when in Act II, which is based directly on the film, she reappears as Little Edie, scuffing around Allen Moyer's deliberately seen-better-days set in the wardrobe that William Ivey Long modeled on the actual Edie's ludicrous fashion notion. Speaking in the demotic accent Edie adopted as she aged and singing with loopy distraction, Ebersole gives not just a remarkable impersonation, but the performance of her life. Which is saying something, because whatever she does, she's always on target.

The same can be said of Mary Louise Wilson, who has jettisoned the lacquered black coiffeur she wore a decade ago as Diana Vreeland (in Full Gallop) for Big Edie's straggly white fashion-don't do. Sounding like a needle scratching across an old 78, Wilson whines demandingly and relents pleadingly as she heats soup by her bedside and drifts between infantilizing and praising her compliant off-spring. Anyone who's seen the 1975 flick will also recognize Wilson's take as an uncannily impressive impersonation.

At its core, Grey Gardens is a close-up-and-personal look at the mother-daughter love-hate relationship. It depicts the extremes to which parent-child co-dependence can extend. By preceding their take on the film with an act taking place 32 years earlier, the musical's creators obviously mean to show the subtle precedents for the Beales' ultimately stultifying relationship. They want to explore psychological universals -- the unconscious inclination of parents to thwart their children's maturation, the competitive nature of old and young. Both Beales play this out as a desire to be singers.

Grey Gardens' move to Broadway has had a curious effect on the tuner. In its earlier incarnation, the first act was a tepid spin on Philip Barry's Philadelphia Story with bright, impassioned Cole Porter-esque ditties tacked on. Although it's still not anything like a knockout curtain-raiser, the act has been sharpened and the foreshadowing of the older Edie's hold on the younger one seems heightened.

In addition, a few songs have been dropped and two of them have been replaced, including one for John McMartin, who plays critical father and granddad, J. V. "Major" Bouvier, with his usual upper-class bluster. Unfortunately, all the songs -- except the Act I closer "Will You?" -- still come across as mild pastiches. (Only "Will You?" would become a standard if shows still had the power to make standards.)

Conversely, the second act -- which actually could stand alone and probably ought to -- currently seems less compelling than it did before, because director Michael Greif has Ebersole and Wilson underline what was already fully realized before. But this is only a minor quibble. Moreover, the Korie-Frankel songs for Act II seem to have been written by a different team altogether -- a quirky duo who especially make hay with Ebersole's "Revolutionary Costume for Today" and "Around the World" and Wilson's "Jerry Likes My Corn."

Decades ago, Variety editor Abel Green warned against fiddling with a hit. Since Grey Gardens was only an almost hit when it bowed, the creative team did need to apply additional elbow grease. Their alterations, however, aren't sufficient to make the property noticeably more or less than it was: a musical to be seen for the brilliant, unflinching second-act performances given by Ebersole and Wilson.